The proposed experiments fall into two areas: cholinergic neurons in the retina and phospholipid renewal by photoreceptor cells. The cholinergic cells have been shown to make up a small subpopulation of the retina's neurons. They are arranged with mirror symmetry around the inner synaptic layer. We now propose to attempt a complete description of the shape of these cells, by using HRP or fluorescent dyes as cell filling agents. The agents will be injected into the retina or introduced into the medium in which the tissue is incubated, and will be visualized by enzymatic reaction or fluorescence microscopy. We are studying phospholipid renewal by studying the consequences of its interruption, using the choline analogue hemicholinium-3 as a means of depriving the cells of a critical phospholipid precursor. We now propose to evaluate the retina's electrophysiological function during the lesion and during recovery, by recording from the ganglion cells during photic stimulation.